As one of the top three leading causes of death among teenagers and young adults, suicide has become an issue of increasing public health concern. Hopelessness has been identified as a cognitive risk factor for suicidal thinking and behavior, but the precise ways of thinking through which hopelessness arises and through which it leads to suicidal thoughts and behaviors is not well understood. This proposal for a SCORE Research Advancement Award seeks to fill this gap in the literature by 1) identifying differences in how two different subtypes of rumination prospectively predict suicidal ideation among previous suicide attempters and non- attempters, 2) examining rumination about the future as another type of process through which individuals develop hopelessness, along with modeling a procedure through which these thoughts might be changed; and 3) examining the specific cognitive content characteristic of hopeless that predicts risk for future suicidal thoughts and behavior. These aims will be addressed via a longitudinal study of a sample of young adults - screened for a history of suicidal ideation and attempts - who complete a battery of cognitive measures over 6, 12, and 18 months. Data will be analyzed via mixed model regression to examine the pathways through which two verbal-linguistic forms of rumination lead to suicidal ideation and behavior. These data will also be analyzed via multi-level modeling to examine whether rumination about the future - assessed with a newly- developed measure - is a procedure through which depressive predictive certainty and hopelessness develop. To examine the third aim, this study will utilize a cognitive fluency paradigm to test the hypothesis that young adults with reduced cognitive fluency in expecting positive future outcomes, along with certainty about an absence of positive outcomes -- are at increased risk of future suicidal ideation and attempts. Finally, individuals with and without a history of suicidal ideation or attempts will be trained to mentally rehearse making optimistic future-event predictions, to determine whether inducing optimistic future expectations leads to reduced depressive predictive certainty and hopelessness among individuals with a history of suicidality.